This disclosure relates to novel aqueous ink-jet inks having improved stability containing an aqueous vehicle, a colorant, and an amphoteric polyurethane as a binder.
Ink-jet printing is a non-impact printing process in which droplets of ink are deposited on a substrate, such as paper, to form the desired image. During ink-jet printing, it is often necessary for the recently printed-article to come into contact with the paper-handling mechanism of the printer, e.g., in the case of duplex printing where both sides of the media are printed. In this situation the first printed side may not yet be completely dry and as a result the print surface can be damaged and the ink can transfer onto the paper-handling mechanism and then onto subsequent prints. This problem is particularly acute when using a wet-press which involves considerable paper-handling at high speeds. Often the press uses heated rollers to transfer media which is prone to having problems as the drying ink sticks to the rollers. Severe problems may be encountered when slow-drying inks are printed onto non-absorbent media such as coated offset media.
Polyurethane dispersion particles are often formulated into ink-jet inks to provide fast drying, improve image durability and/or image quality such as inter-color bleed and image uniformity. The physical properties such as viscosity and pH of ink-jet inks containing anionic polyurethane particles tend to change upon storage over time especially after oven aging at elevated temperatures. A need exists for highly stable ink-jet inks that can be printed on various substrates to form durable, high quality image. The present disclosure satisfies this need by providing ink compositions containing an amphoteric polyurethane dispersion where the amphoteric polyurethane contains a plurality of tertiary amine groups derived from an amine-containing monomer and a plurality of anionic acid groups.